138 CHEMICAL STATICS 



would doubtless be formed. In the majority of investigations 

 upon this subject no care has been taken to maintain a neutral or 

 otherwise constant reaction in the medium from which the protein- 

 heavy metal compound is thrown out, each observer has prepared 

 these compounds under different conditions, and no clear dis- 

 tinction has been made between the precipitation of the protein by 

 the heavy metal salt and its coagulation. It is not matter either 

 for surprise or bewilderment, therefore, that different observers 

 have obtained very conflicting results in determining the heavy 

 metal content of these compounds. In the light of our present 

 knowledge the majority of these results are perceived to be mean- 

 ingless, since they were obtained with compounds, or mixtures of 

 different compounds, prepared under inadequately controlled 

 conditions.* 



From the observations of Galeotti (30), we may infer that at 

 the moment when precipitation begins, the compound of egg-albumin 

 with silver (or silver nitrate) is of constant molecular weight and 

 solubility in water. This investigator has applied to the system 

 protein, egg-albumin, water, the law of Jahn, that the influence 

 which an electrolyte exerts upon the solubility of another substance 

 (its dehydrating or hydrating action) is a function of three vari- 

 ables, namely, the concentration of the undissociated molecule of 

 the electrolyte, that of its cation, and that of its anion. Gal- 

 eotti measured the percentage of protein precipitated and also the 

 concentration of silver ions, determining the latter directly with 

 the aid of a concentration-chain (potentiometer). Calling C the 

 molecular concentration of a saturated solution of the protein- 

 silver-nitrate, and C' its solubility in the presence of silver nitrate, 

 applying Jahn's law we have 



lognat. = [CotK + C k fou + 



in which R is the gas-constant; <foi (at constant temperature and 

 pressure) is the constant ratio between the concentration of the 

 non-dissociated molecule of AgNOs and its effect upon the solu- 

 bility of the protein-compound; $n and <fci are similar factors for 

 the cation and the anion of the silver nitrate; and C and Ck are 

 the concentrations, respectively, of the undissociated and the 



* For a review of the older literature upon the heavy metal compounds of 

 proteins, Cf. O. Cohnheim (25). 



